The upper respiratory tract plays an important role in acclimatizing the inhaled gas as the respiratory epithelium of the lower respiratory tract changes towards the terminal bronchioles, successively decreasing the capability to humidify and warm the inspired gas. During anaesthesia, however, the upper respiratory tract is bypassed by endotracheal intubation or a laryngeal mask, leaving the lower respiratory tract potentially overcharged with the task of adequately acclimatizing the cold and dry gas applied during high flow anaesthesia. Mechanical ventilation with cold and dry gas can thus lead to damage of the lung parenchyma.

Cold and dry respiratory gases reduce ciliary activity in the respiratory epithelium. The reduction of mucociliary clearance can lead to atelectasis and infections, conditions referred to as postoperative pulmonary complications. Warming and humidifying the respiratory gases using low-flow anaesthesia can reduce these negative effects on the respiratory epithelium.